Mount Everest's height increases each year: Here's why

Mount Everest, the tallest peak on Earth, remains a symbol of awe, adventure, and the forces that shape our planet. At 29,032 feet (8,849 meters), it dominates the Himalayas and surpasses K2 by around 800 feet. While its presence is well known, the mechanisms behind its growth are less so. Recent research reveals a surprising contributor to Everest’s height: a distant river carving through the landscape.

River erosion boosts Everest's height

Scientists know the Himalayas, including Mount Everest, began forming around 45 million years ago when the Indian tectonic plate collided with the Eurasian plate, causing the crust to crumple and lift into mountains. While this tectonic activity explains the initial rise, it doesn’t account for the ongoing growth observed today.

“Mount Everest is a mountain of myth and legend, and it’s getting bigger,” said Adam Smith, a geoscientist at University College London and co-author of the new study. “Our research shows that as the nearby river system gets deeper, the loss of material is causing the mountain to rise even higher.”

The mystery deepened when researchers from the China University of Geosciences and University College London examined forces beyond simple tectonics. Their findings, published in Nature Geosciences, point to the Arun River, 75 kilometres east of Everest, as a significant player.

Over thousands of years, the Arun River has carved a vast gorge and transported immense sediment downstream. The river’s erosion thins the crust in the region, leading to “isostatic rebound,” allowing the Earth’s mantle— a dense, semi-fluid layer beneath the crust— to push upward as it compensates for the reduced weight above.

Xu Han, the study’s lead author, explained, “The changing height of Mount Everest highlights the dynamic nature of the Earth’s surface. The interaction between erosion from the Arun River and the upward pressure of the Earth’s mantle boosts Mount Everest, pushing it higher.”

Crust rebound lifts Everest slowly

Isostatic rebound occurs when the Earth’s crust, having lost weight due to erosion or melting ice, flexes upward. This is like a mattress springing back when pressure is lifted. In Everest’s case, the thinning of the crust under the Arun River’s excavation pressure allows for a subtle but continuous uplift of the mountain, approximately 2 millimetres per year.

Matthew Fox, another researcher, noted, “Mount Everest and its neighbouring peaks are growing because isostatic rebound is raising them faster than erosion is wearing them down. They’re growing by about two millimetres a year using GPS instruments and we now understand what drives this growth.”

The Arun River’s impact story began 89,000 years ago with a geological event called “drain piracy,” where the river annexed the Kosi River. This merger amplified the Arun’s erosive power, allowing it to carry away more sediment. The subsequent loss of crustal mass permitted the buoyant mantle below to exert a more significant upward force.

“Although mountains may seem still from a human lifetime perspective, they are constantly in motion,” said Jin-Gen Dai, a geoscientist from the China University of Geosciences and a co-author of the paper. This movement underscores the ever-changing nature of Earth’s crust and the hidden dynamics beneath its surface.

Everest and neighbours grow, erosion impacts

Research indicates Everest isn’t alone in its ascent. Neighbouring peaks, Lhotse and Makalu—the fourth and fifth highest mountains—are also growing due to the same isostatic rebound effect. Notably, Makalu, nearer to the Arun River, appears to be rising slightly faster than Everest.

The findings emphasize how a river’s erosive power can shape the landscape and alter the elevations of entire mountain ranges over millennia.

While Everest and its neighbours’ growth is well documented, researchers believe it might not continue indefinitely. As erosion and tectonic processes fluctuate, the forces’ balance could shift, potentially slowing or reversing the uplift.

“The rocky skin of a dynamic planet is never stationary. Over long time scales, it’s almost as if the Earth is breathing,” Adam Smith said, summarizing the equilibrium between upward mantle pressure and surface erosion.

New insights into Mount Everest’s growth remind us that our planet, though seemingly stable on human time scales, is perpetually evolving. The interplay of deep mantle dynamics, river erosion, and crustal movement contributes to a richer and more complex narrative. 

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